How many total circles will be used if there are 20 rows of circles? show all calculations.

210

Step-by-step explanation:

As there is one circle in first row, 2 circles in 2nd row and three in third row, which clearly implies that the number of circles in each row is equal to the row number. So, we have to calculate sum of first 20 numbers to calculate the total number of circles.

n=20

Total Circles=(n(n+1))/2

=(20 (20+1))/2

=(20(21))/2

=  420/2

=210

So the total number of circles will be 210.  

walter needs to make at least 5 more cookies but no more than 40. 5 ≥ x ≥ 40;

step-by-step explanation:

walter has to make a minimum of 20 cookies. he already has 15 cookies made, so he must make 5 more to meet the minimum.

the maximum amount of cookies he can make is 55. he already has 15, so he has to make no more than 40 more cookies to meet the maximum.